RE: Runaway z axis with steppers

[wb9mjn <wb9mjn-at-wb9mjn-11.ampr.org>]

  Hi Ray,

       The input scales on all three axis is the same on my machine. It is 
a 1 mm pitch machine, with 10X microstepping steppers. All three axis have 
input_scale and output_scale set to 2000.  0.   .

       If I remember correctly, the problem would happen on the MDI 
commands too, until I set the I and D to 0, as well as the the P to 1500.

      73, Don...


-----Original Message-----
From:	Ray Henry [SMTP:rehenry-at-up.net]
Sent:	Saturday, September 07, 2002 2:08 PM
To:	Multiple recipients of list
Subject:	Re: Runaway z axis with steppers



Hi Don.

Thanks for that confirmation.  I was beginning to think that it was me!
What input_scale value are you using on Y?

Ray



On Saturday 07 September 2002 01:32 pm, you wrote:
>   Hi Ray,
>
>         Yes, I have this problem too on a BDI/TNG implementation. But
> it is on my Y axis. Setting the P to 1500 minimized (eliminated?) it
> for MDI and AUTO commands. But it still happens after the first or
> second manual command to the Y axis.
>
>       73, Don...
>
>
> -----Original Message-----
> From:	Ray Henry [SMTP:rehenry-at-up.net]
> Sent:	Saturday, September 07, 2002 11:26 AM
> To:	Multiple recipients of list
> Subject:	Runaway z axis with steppers
>
>
> EMC List
>
> I posted this a while back to the developers list at sourceforge but I
> don't think that that list is working so I'll post it here.
>
> Attached is an ini from Tim <tim.smith-at-electrolux.com.au> that does
> some goofy stuff here.  I'm not exactly going to call it a bug, rather
> the odd behavior is the product of certain combinations of values in
> the ini file when used with freqmod.o.  The same behaviors are not
> obvious with steppermod.
>
> I'm started testing this with TNG with no machine attached to the
> parport. I think I'd be afraid to start much of a machine with this
> setup because it trips up the stepper math and creates an oscillator
> that tends to push an axis slowly in a single direction -- even when no
> motion is commanded.  With the attached ini file, I see this behavior
> after a couple of quick jogs of the Z axis.
>
> I've also tested this behavior with BDI-2.16 and my Grizzly minimill
> and it seems to behave the same as the TNG.
>
> Here is what I did to exhibit the problem.
>
> Startup using timsfreq.ini.  (attached)
> Start the machine and home out.
> Start scripts->IO_Exercise to view parport 0x378. (default)
> Issue a couple of quick jogs in Z
>
> Once the problem shows up with the IO_Exercise display and I press
> estop, the step pin seems to latch but the displayed position runs
> wild.
>
> The problem seems to go away if scale is set about 20 with a proper
> deadband.  It also goes away or changes the way it works with larger
> gains and different combinations of velocities and accelerations.
>
> With some small adjustments, the problems seems to change into a simple
> dither between adjacent steps but as it is, all of the steps are in the
> same direction.
>
> I need someone to see if they can reproduce this problem and work with
> me to clearly define the nature of it.
>
> Ray
>
>
>
>  << File: timsfreq.ini >>